1. Field of the Invention
The invention relates to a method for heating a low-temperature-carbonization drum, in particular a carbonization drum for a low-temperature-carbonization combustion process, in which heating gas that is heated in a heat exchanger is carried in a heating gas loop from the heat exchanger to the carbonization drum and from there back to the heat exchanger, and in which there is a heat sink for cooling down the heating gas. The invention also relates to an apparatus for heating a carbonization drum, particularly a carbonization drum for the low-temperature-carbonization combustion process, which is disposed together with a heat exchanger in a heating gas loop for heating gas, and which communicates there with a heating gas feed line and a heating gas outlet line, with a heat sink being provided for cooling down the heating gas.
2. Description of the Related Art
Published European Application No. 0 302 310 A1, corresponding to U.S. Pat. No. 4,878,440, discloses a method and a system for thermal waste disposal. The system described therein has a carbonization drum, which is referred to as a "pyrolysis reactor". That kind of system is also known from German Published, Non-Prosecuted Application DE 38 15 187 A1. In order to heat the carbonization drum, the drum is supplied with a heating gas. The heating gas is carried in the carbonization drum in tubes. There, it gives up heat energy to the material to be carbonized. A loop in which the heating gas is carried includes a heat exchanger, with which thermal energy is supplied to the heating gas. In a low-temperature carbonization combustion system, the heat exchanger may, for instance, be disposed on the combustion chamber. The heating gas then takes thermal energy from hot flue gas.
The known heating apparatus is constructed for a typical heat requirement in the carbonization drum. For instance, it may be assumed that a calorific value of the material to be carbonized lies between 6500 kJ/kg and 15000 kJ/kg.
If a material with a high calorific value, which is markedly above the typically present calorific value, is to be carbonized, then only little or no heat energy can be drawn from the heating gas in the carbonization drum. That is particularly true if the carbonization drum is driven at full load.
It is also known from German Published, Non-Prosecuted Application DE 38 15 187 A1 to use an additional heat exchanger as a heat sink, in which all of the heating gas is cooled down in the heating gas loop in a direct path between the heat exchanger and the carbonization drum. The additional heat exchanger is regulated on the secondary side, which as a rule is rather expensive. In other words, special heat exchangers are required that can be regulated on the secondary side. Moreover, heating gas that has already flowed through the carbonization drum and has therefore cooled down can be fed directly back into the heating gas line of the carbonization drum so as to lower the heating gas temperature there.